In the deep cooling of articles and materials, e.g. rubber tires or synthetic-resin scraps to enbrittle them prior to comminution or also in the preparation of frozen foods and the like, it is known to contact the objects, namely, the articles and materials, with a cooling gas by direct heat exchange.
In prior-art processes of this type, the objects can be cooled to a point in which they are embrittled sufficiently to allow the comminution or milling thereof.
In commonly assigned application Ser. No. 648,100 filed Jan. 12, 1976 by two of the present joint inventors (now U.S. Pat. No. 4,072,026), there is described a combined cooling process in which the objects are passed in counterflow to a first cooling-gas stream over part of the cooling zone and a low-temperature or deep-cooling second gas stream is introduced at the cold end of the zone and has a substantially lower temperature than the first gas stream. After heat exchange with the objects or materials in the deep-cooling zone, the two gas streams are mixed within a region of the cooling path.
This combined cooling process, which has considerable advantages over still earlier systems, is characterized by the primary advantage that the necessary low temperature can be generated from two independent sources as required by the conditions to be maintained in the cooling path.
This permits the delivery of a large amount of cold to the apparatus and enables the apparatus to be able to handle different cooling rates, various materials and the like.
Experience with this combined process has, however, shown that the temperature distribution along the cooling path can be readily adjusted to suit the particular objects to be cooled but that this is only the case when the mixing of the two gas streams in the cooling path is carried out such that they have the same temperature. This can only be achieved by varying the position and nature of the mixing zone within the cooling path and by admitting the first cooling-gas stream into the cooling path at various locations, or by using relatively expensive control systems for the two gas streams.